Do not treat as minor. If the engine runs with no limp or safety lights active, drive only far enough to get it diagnosed; a genuine CAN-C bus-off fault can strand the vehicle or disable ABS and stability control without warning. U0002 is a performance/bus-off fault on the high-speed CAN-C communication bus — the 500 kbps two-wire backbone that links the powertrain, ABS, and other high-priority modules. Unlike a simple missing message, this code means a module (usually the Body Control Module) has seen the bus circuit itself shorted or dragged into a bus-off state, so it is a bus-integrity problem in the shared wiring, star connectors, or a module loading down the network — not a fault buried inside one named component.
What U0002 means
The high-speed CAN-C bus is a twisted pair — CAN-High and CAN-Low — that carries time-critical data at 500 kilobits per second, while a slower 125 kbps interior bus handles lower-priority traffic; the Body Control Module acts as the central gateway between the two. During normal operation the pair idles at roughly 2.4–2.5 V on both wires (recessive) and swings to about 2.6–3.5 V on CAN-High and 1.3–2.3 V on CAN-Low when a message is active (dominant). U0002 sets when the reporting module detects a short on one of the CAN-C circuits — CAN-High to ground, CAN-Low to voltage, or the two wires shorted together — or when the bus is corrupted badly enough to go bus-off. When an open or terminal push-out isolates a module, that controller keeps trying to talk without proper arbitration and alters the bus voltage while other messages are in flight, corrupting traffic for everyone on the segment. Because the fault lives in the shared circuit rather than one component, U0002 points you at the harness, star connectors, terminating resistors, and module power/grounds first.
Symptoms
- Several warning lights on together — check-engine, ABS, traction/stability, and often airbag or steering lamps — as multiple modules lose their shared data at the same instant
- A spread of U-codes stored across different controllers (bus-off and lost-communication faults) that all show up together on a full-system scan
- Reduced-power or limp-home behavior as modules fall back to safe defaults when high-speed traffic drops out
- Erratic or frozen gauges, warning lamps, HVAC, or infotainment as bus messages come and go intermittently
- Hard-start, crank-no-start, or a no-crank condition if the powertrain and immobilizer messages cannot get through
- A scan tool that is slow to connect, or that shows one or more modules in red on the network review screen
Common causes
- The CAN-C High circuit shorted to ground — chafed, pinched, or crushed harness wiring is the most common trigger
- The CAN-C Low circuit shorted to battery voltage, pulling the differential signal out of range
- CAN-High shorted directly to CAN-Low, collapsing the two-wire signal (bus resistance drops below spec)
- A damaged star connector or a failed terminating resistor internal to a star connector, so the pair no longer reads its expected ~60 Ω
- A single module on the segment failing internally or with a bad connector, loading down or shorting the bus (confirmed only by disconnecting modules one at a time)
- Corroded, backed-out, or water-intruded terminals at a splice, star connector, or module on the bus
- Prerequisite faults — battery-voltage, ignition-run, or VIN-broadcast message codes, or an incorrectly configured BCM — that must be cleared before this code can be validated
Severity & driving advice
Severity: High — The high-speed bus carries engine, brake, and stability data, so a real CAN-C short or bus-off can cause no-start, limp mode, or loss of ABS/ESC.
Can I drive? Do not treat as minor. If the engine runs with no limp or safety lights active, drive only far enough to get it diagnosed; a genuine CAN-C bus-off fault can strand the vehicle or disable ABS and stability control without warning.
Diagnostic approach
- Run the pre-diagnostic and confirm the code is active — Perform the communication pre-diagnostic/pre-troubleshooting routine first, then turn the ignition on and read all modules. U0002 is monitored with the key on (the module version validates it with ignition run time over one second, battery between 9 and 16 V, and engine run time over three seconds). Use the scan tool network review screen — faulted areas show in red and point to the source.
- Separate an active fault from an intermittent one — Record and erase the DTCs, cycle the ignition from on to off three times, then re-read. If U0002 returns as active, chase the hard short below; if it stays gone, the fault is intermittent — inspect every related splice, star connector, and connector for water intrusion, corrosion, pushed-out or bent terminals, and correct pin tension before closing out.
- Fix prerequisite codes and verify BCM power/ground and configuration — Repair any stored battery-voltage, ignition, or VIN-message faults and confirm the Body Control Module is configured correctly with healthy power and grounds. A weak feed or poor ground can pull the BCM or the reporting module off the bus and mimic a bus short, and the factory bus test is only valid once these prerequisites are satisfied.
- Check the CAN-C Low circuit for a short to voltage — With the scan tool disconnected and the ignition on, measure between ground and the CAN-C Bus (-) circuit. A reading above about 10 V indicates the negative circuit is shorted to voltage; use the star connectors to split the bus into sections and find whether the wiring is at fault or a specific module is the source, then repair or replace whichever restores normal voltage.
- Check the CAN-C High circuit for a short to ground — Measure between ground and the CAN-C Bus (+) circuit. Roughly 0 V means the positive circuit is shorted to ground (a healthy CAN-High short-to-ground reads near 0.02 V). Again isolate the bus at the star connectors to localize the short, and repair the harness or replace the offending module.
- Verify termination resistance across the pair — Turn the ignition off and disconnect the negative battery cable, then measure resistance between CAN-C Bus (+) and CAN-C Bus (-). A healthy network reads between about 53.5 and 67 Ω (the two 120 Ω terminators inside the star connectors sit in parallel for ~60 Ω). Above 67 Ω means an open, high resistance, or a damaged internal terminator; below 53.5 Ω means the two wires are shorted together — isolate at the star connectors to pinpoint it.
- Isolate a suspect module, repair, then run the verification test — If wiring and terminators check out, disconnect modules on the segment one at a time and re-measure; the fault clearing when a specific controller is unplugged identifies it as the source (note that disconnecting the RF hub module drops ignition-status messages and can upset scan-tool communication). After the repair, clear all modules, perform the body verification test, cycle the key, and drive through the set conditions to confirm the code stays gone network-wide.
FAQ
How is U0002 different from U0001?
Both are high-speed CAN-C bus-integrity codes, but U0002 is the performance/bus-off variant — the reporting module has detected an actual short on a CAN-C circuit or the bus corrupted into a bus-off state, whereas U0001 is the broader general-bus-fault code. On Stellantis vehicles an active U0001 routes into the U0002 CAN C Bus Off Performance diagnostic, so they are documented as siblings and often appear together.
How is U0002 different from U0100 and the other lost-communication codes?
U0002 describes a problem with the shared CAN-C bus circuit itself — a short or bus-off affecting the whole pair. The U01xx codes such as U0100 name one specific module (for example, lost communication with the ECM/PCM). U0002 is broader and usually shows up alongside a cluster of those module-specific codes when the shared bus goes down.
What resistance should the CAN-C bus read across the two wires?
With the battery disconnected, measure between the CAN-C (+) and CAN-C (-) circuits; a healthy network reads roughly 60 Ω, and the factory acceptable window is about 53.5 to 67 Ω. A reading above 67 Ω points to an open, high resistance, or a damaged terminating resistor inside a star connector, while a reading below 53.5 Ω means the two wires are shorted together.
What are the normal CAN-C bus voltages?
At rest (recessive/idle) both CAN-High and CAN-Low sit around 2.4–2.5 V. When a message is active (dominant), CAN-High rises to roughly 2.6–3.5 V and CAN-Low drops to about 1.3–2.3 V. If the negative circuit reads above 10 V it is shorted to voltage, and if the positive circuit reads near 0 V it is shorted to ground.
Can U0002 cause a no-start?
Yes. The high-speed CAN-C bus carries the messages the engine controller and immobilizer need to run. If the bus is shorted or goes bus-off, that data can never arrive, so the vehicle may crank without starting or refuse to crank until the bus fault is repaired.